The present invention relates to transceivers and, more particularly, to battery powered transceivers with battery monitoring circuits.
As used herein, "transceiver" includes radiotelephones and cordless telephones.
The increasing use of rechargeable batteries in electronic and electromechanical equipment has stimulated the development of methods of preventing such batteries from being excessively discharged. The importance of this precaution stems from a number of factors related to battery life and rechargeability. The major factors are the irreversible, deleterious changes that take place within most batteries when they are deeply discharged, changes which not only prevent the battery from being subsequently recharged to its full ampere-hour capacity, but also eventually lead to battery failure as a result of repeated deep discharges.
An additional factor is the increasingly steep decline in battery voltage and the sharp rise in internal battery resistance as a battery approaches a condition of deep discharge. This resistance becomes an increasing portion of the dissipative, parasitic load, and a battery so abused rapidly loses its ability to maintain its terminal voltage under even a modest load. A further factor is the disproportionate lengthening of the time required for recharge of such batteries; relatively brief periods of use when the battery is approaching a deeply discharged condition may add hours to the time needed for recharge. Unfortunately, a battery which cannot be recharged overnight, and which requires up to 24 hours to recharge, will seldom be kept charging for the period necessary to obtain a full charge. More often, the battery will be removed from the charger and will be put into service though only partially recharged, and this can result in a memory factor limiting the amount of charge which the battery will subsequently take.
A variety of methods have been devised to monitor the terminal voltage of rechargeable batteries in order to sense when they are approaching deep discharge, and, along with control circuitry, to limit battery drain or even completely disconnect the load from the battery whenever the monitored voltage is sensed to have fallen below a desired threshold voltage.
The focus of most of these methods is an economic concern to prevent the battery from being damaged to the point where recharge is impossible and the battery must be replaced. In some instances, another concern is to minimize the inconvenience of an interruption in service. The prior art has not recognized the impact of inability to make use of equipment under circumstances when the failed or deeply discharged battery imperils the safety or even the survival of the user and others.
Such circumstances are frequently encountered in marine, police and fire applications. On small craft operating offshore, the only means of communication may be a hand-held radiotelephone or transceiver operating on a rechargeable battery. Radiotelephones used on such small craft serve several vital functions aside from that of ordinary communication, one of the major functions being to monitor the Coast Guard emergency channel (VHF Channel 16), since it is on that channel that safety messages, small-craft warnings and distress calls are broadcast, as well as initial hailing calls are received. Another major function is to permit the transmission of requests for emergency assistance on that channel, since it is monitored by the Coast Guard as well as by other craft which may be nearby and able to assist.
The rapidity of weather changes offshore is well known; the transition of the weather from light breezes to a dangerous, if short-lived squall, may occur within a period of half an hour or less. Therefore, small craft operators typically keep their radiotelephone receivers on and tuned to the emergency channel to hear any small-craft warnings, distress calls or other weather alerts. A substantial portion of the battery power is generally consumed in this manner, and a further drain is the power drawn by the transmitter during operation.
Engine failure or other malfunction is another common occurence with small craft which can deprive them of the headway needed for steering and put them in danger of capsizing as weather worsens. At such times sufficient battery power for the broadcast of requests for emergency assistance may constitute the margin between life and death. Clearly the power consumed in monitoring the emergency and other channels may, in such circumstances, place in jeopardy the adequacy of battery power needed for emergency transmissions.
It is therefore apparent that the monitoring for distress calls and warnings which is essential to safety offshore may be the cause of serious depletion of battery power, posing the danger of communications cutoff. Thus, paradoxically monitoring for safety broadcasts may ultimately threaten the safety of the vessel's occupants. When this situation is aggravated by having a battery which, because of earlier deep discharges, has not or cannot be fully recharged, the danger is sharply increased.
It is an object of the present invention to provide a novel battery-powered radiotelephone having both a battery-saver feature to prevent deep discharge and a battery power conservation feature to reduce the power consumption during channel monitoring and the time for recharging.
It is also an object of the present invention to provide a radiotelephone in which such features are automatically operative so that the benefits are not dependent upon the actions or operating procedures of the user.
Another object is to provide such a radiotelephone in which such features are provided relatively economically by components which are relatively simple and long lived.